Cfd

BRAYTON – Computational Fluid Mechanics with Experimental Validation Recirculating flow

Skewness Factor for Various Inlet-Header Widths (fixed exit-header width = 5.0in) 10.0%

Skewness Factor is (∆ ∆pMAX - ∆pMIN) / ∆pAVG from linear fit to data

8.0%

6.0%

Skewness Factor

4.0%

+ skewness is biased toward centerline (away from inlet) 2.0%

Wh = 1.5in Wh = 3.0in Wh = 4.5in

0.0%

-2.0%

-4.0%

-6.0%

Exit flow separation

This analysis sponsored by AREVA

-8.0% 0.3

0.4

0.5

Reynolds Number

0.6

0.7

0.8

0.9

1.0

Manometer Bank

Flow Normalized by Design Value

Flow Meter

Regenerative Blower

Cell Inlet Cell Outlet

Rigorous experimental technique – Quality of Data

Flow distribution on rectangular slot headers – a CFD analysis validated with experimental methods • •

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Counterflow heat exchangers require cross-flow headers to properly orient one or both of the fluid streams in the counterflow matrix. The geometry of the inlet and exit headers introduce regions of separated flow, thickened boundary layers, turning losses, and entrance and exit effects. These factors influence the flow distribution within the counterflow matrix as well as the headers’ pressure loss. Due to the complexity of the flow field, standard header design correlations are not suitable. The typical engineering approach is to conservatively over-size the header dimensions to assure low losses and uniform static pressure distribution between the entering and exiting faces of the counterflow matrix. However, increasing header width is known to elevate thermal stresses at the interface between the matrix and the header. With the objective of minimizing header dimensions, Brayton has performed a series of parametric studies on a practical header geometry. These studies quantify the flow distribution through the counterflow matrix, predict overall pressure losses, and derive the velocities necessary to determine local heat transfer coefficients. A combination of computational fluid dynamic (CFD) and controlled experimental methods are employed to analyze the headers and optimize the geometry for acceptable levels of stress levels, pressure losses, and flow mal-distribution. Though CFD is an invaluable tool, we believe that it’s results are often more qualitative that quantitative. In most cases, experimental methods, with rigorous attention to details is required to adjust internal turbulence models and validate CFD models Brayton Energy performs a full service of CFD analyses. We also take special pride in our understanding of experimental methods and the importance of maintaining the highest possible testing standards.